(x-80) * 40 = 640
40х - 3200 = 640
40х = 640 + 3200
40х = 3840
х = 96
(х - 80) : 40 = 640
x/40 - 80/40 = 640
x/40 -2 = 640
x - 80 = 25600
x = 25600 + 80
x = 25680
(x-80) * 40 = 640
40х - 3200 = 640
40х = 640 + 3200
40х = 3840
х = 96
(х - 80) : 40 = 640
x/40 - 80/40 = 640
x/40 -2 = 640
x - 80 = 25600
x = 25600 + 80
x = 25680